1. Field of the Invention
Embodiments described herein relate generally to a pattern inspection apparatus and a pattern inspection method. For example, embodiments described herein relate generally to an inspection apparatus and method that inspect a pattern by acquiring an optical image of a pattern image through irradiation of laser light.
2. Related Art
In recent years, with increasingly higher degrees of integration and larger capacities of large-scale integration circuits (LSI), circuit line widths demanded for semiconductor devices become increasingly narrower. Such semiconductor devices are fabricated by exposing and transferring a pattern onto a wafer by step-and-repeat equipment, the so-called stepper, to form a circuit using an original pattern (also called a mask or reticle; hereinafter, collectively called a mask) in which a circuit pattern is formed. Thus, to manufacture a mask for transferring such a fine circuit pattern to a wafer, a pattern writing apparatus capable of writing a fine circuit pattern and using an electron beam is used. By using such a pattern writing apparatus, a pattern circuit may directly be written onto a wafer. Alternatively, the development of a laser beam writing apparatus that writes by using a laser beam, in addition to the electron beam, is attempted.
The improvement of yield is indispensable for manufacturing LSI requiring a large amount of manufacturing costs. However, as is typically shown by DRAM (Random Access Memory) of 1 gigabit or so, patterns constituting LSI are in transition from the order of submicron to that of nanometer. One of the major causes that decrease the yield is a pattern defect of the mask used when a superfine pattern is exposed and transferred onto a semiconductor wafer by photolithography technology. With increasingly finer LSI pattern dimensions formed on the semiconductor wafer in recent years, dimensions that need to be detected as pattern defects are also extremely small. Therefore, a pattern inspection apparatus that inspects for defects of a transfer mask used for manufacturing LSI needs to be made more precise.
On the other hand, with the development of multimedia, the liquid crystal substrate size of LCD (Liquid Crystal Display) increases to 500 mm×600 mm or more and patterns of TFT (Thin Film Transistor) or the like which are formed on a liquid crystal substrate become increasingly finer. Thus, it becomes increasingly demanded to inspect for extremely small pattern defects in a wide range. Therefore, the development of a pattern inspection apparatus that inspects efficiently in a short time patterns of such a large-area LCD and that inspects for defects of a photomask used when a large-area LCD is produced is also urgent.
As an inspection method, a method of conducting an inspection by comparing an optical image obtained by capturing an image of a pattern formed on a target object like a lithography mask in a predetermined magnification by using an magnifying optical system with design data or an optical image obtained by capturing an image of the same pattern on the target object is known. Examples of the pattern inspection method include the “die to die inspection” that compares optical image data obtained by capturing an image of the same pattern in different places on the same mask and the “die to database inspection” in which writing data (design pattern data), which is converted into an apparatus input format used for a writing apparatus to input pattern-designed CAD data when writing a pattern on a mask, is input into an inspection apparatus, and based on the design pattern data, design image data (reference image) is generated to compare the reference image and an optical image to be measured data obtained by capturing an image of a pattern. In such inspection methods in the inspection apparatus, a target object is placed on a stage and an inspection is conducted by scanning the target object with a luminous flux as the stage moves. The target object is irradiated with the luminous flux by a light source and an illumination optical system. Light transmitted through or reflected by the target object forms an image on a sensor via an optical system. The image captured by the sensor is sent to a comparator as measured data. After images are aligned, the comparator compares the measured data and reference data according to an appropriate algorithm and determines that there is a pattern defect if the measured data and the reference data do not match.
When patterns become still finer in the future, an inspection apparatus that inspects cell portions including fine patterns of less than the resolution limit that are difficult to resolve by deep ultra-violet (DUV) light and a corresponding optical system will be needed. On the other hand, an inspection of pattern defects in a size that can sufficiently be resolved is simultaneously needed. Unfortunately, in the related art there has been such a problem that there exists neither apparatus nor method that can adequately be used for both of an inspection of fine patterns of less than the resolution limit and an inspection of pattern defects in a size that can sufficiently be resolved in accordance with precision.
As a technology related to an inspection apparatus that inspects cell portions, a technology using both of a cell comparison inspection that compares cells including a pattern in a size that can sufficiently be resolved and the aforementioned die to die inspection is disclosed (see Published Unexamined Japanese Patent Application No. 2005-274172, for example). However, it is difficult for such an inspection apparatus to inspect fine patterns of cell portions of less than the resolution limit.
As described above, there has been such a problem that there exists neither apparatus nor method that can adequately be used for both of an inspection of fine patterns of less than the resolution limit and an inspection of pattern defects in a size that can sufficiently be resolved. However, a satisfactory technique capable of solving such a problem has not been established.